Magnetron atomization source and method of use thereof

ABSTRACT

For optimizing the yield of atomized-off material on a magnetron atomization source, a process space, on the source side, is predominantly walled by the atomization surface of the target body. The magnetron atomization source has a target body with a mirror-symmetrical, concavely constructed atomization surface with respect to at least one plane and a magnetic circuit arrangement operable to generate a magnetic field over the atomization surface. The magnetic circuit arrangement includes an anode arrangement, a receiving frame which extends around an edge of the target body and is electrically insulated with respect thereto. The receiving frame has a receiving opening for at least one workpiece to be coated. The magnetron source can be used to provide storage disks, such as CDs, with an atomization coating.

BACKGROUND AND SUMMARY OF THE INVENTION

[0001] The present invention relates to a magnetron atomization sourcehaving a target body with a mirror-symmetrical, concavely constructedatomization surface with respect to at least one plane, a magneticcircuit arrangement operable to generate a magnetic field over theatomization surface, including an anode arrangement, a receiving framewhich extends around an edge of the target body and is electricallyinsulated with respect thereto, which receiving frame has a receivingopening for at least one workpiece to be coated, and on the side of thesource, a process space bounded essentially by the atomization surfaceof the target body and a surrounding non-atomized residual interiorsurface of the receiving frame. Moreover, the present invention relatesto a method of use thereof in which storage disks, such as CDs, areprovided with an atomization coating.

[0002] Magnetron atomization sources are generally described in DE-OS-2431 832; EP-A-0 330 445; EP-A-0 311 697; U.S. Pat. No. 5,164,063; andDE-PS-40 18 914.

[0003] DE-PS-35 06 227 describes an improved magnetron atomizationsource which has one or two target bodies forming a centricallymirror-symmetrically concavely constructed atomization surface. Aworkpiece which, in top view, has a significantly smaller diameter thanthe diameter of the cup-shaped target body is inserted by way of aholding device for the purpose of atomization coating. Magneticcircuits, which are an arrangement of active elements such as permanentmagnets and/or electromagnets, as well as of passive elements such asferromagnetic elements, for example, of iron yoke parts and air gaps areprovided to generate a magnetic field of the type basically known in thecase of magnetrons. The magnetic circuits operate separately for thebottom area of the atomization surface and its arched edge area,respectively.

[0004] DE-A-28 24 289 describes the atomization surface of a target bodyon a magnetron atomization source in a centrically concave manner and anearth shielding frame in the edge area of the target body. With respectto the target body, the anode is arranged centrically and is cooled by amedium. In this source, a workpiece to be coated is generally arrangedabove the illustrated source. That is, the workpiece is arranged abovethe earth shielding frame which surrounds the edge of the target body.

[0005] EP-A-0 393 957 discloses a magnetron atomization source which hasa centrically concavely shaped-in atomization surface of the targetbody. A workpiece to be atomization-coated is arranged far away from thesource.

[0006] In many cases and specifically also in the case of the use of themagnetron atomization surface preferred according to the presentinvention for the coating of storage disks, for example, of opticalstorage disks (such as magneto-optical disks), video disks or audiodisks (such as compact disks), short coating times with long servicelives of the used target bodies must be achieved. This requirement hasthe effect, among other things, that as a high proportion as possible ofthe material atomized from the atomization source is deposited as acoating material on the workpiece surface to be coated.

[0007] Known atomization sources of the type mentioned above have adisadvantage, however, that, because of, among other things, the largesurfaces which are neither an atomization surface of the atomizationsource nor a surface of a workpiece to be usefully coated, a relativelyhigh percentage of the material atomized from the atomization surface ofthe target is uselessly deposited on other surfaces defining the processspace. This useless deposition drastically reduces the above-mentionedyield, and significantly reduces the coating speed as well as theservice life of a target body. As a result, per target body fewerworkpieces can be coated with the given layer thickness.

[0008] In addition, more cleaning intervals are required in order toensure operational reliability, and higher operating power is requiredto implement desired rates. In turn, thermal stress to the source and tothe workpieces is increased. All of the foregoing has a negative effecton the efficiency of a production system.

[0009] The above-mentioned disadvantages also apply to the magnetronatomization source described in DE-A-42 02 349 which has a centricallyconcavely constructed target body, a magnetic circuit arrangement whichgenerates a magnetic field above the atomization surface, an anodearrangement, and a receiving frame which surrounds the edge of thetarget body and is electrically insulated with respect to it and has areceiving opening for a workpiece disk to be coated. In this knownsource, the process space is defined essentially by the atomizationsurface of the target body and the interior surface of the receivingframe. During operation, the process space is closed off by theworkpiece disk placed on the receiving opening of the receiving frame.

[0010] Considering the fact that the conventional receiving frame, as anexample of a surrounding non-atomized residual interior surface, extendson the outside around the edge of the target body, the length of the cutof the interior frame surface already visible in the cross-sectionresults in a large ring surface which is neither usefully atomized norusefully coated. It is not significantly smaller than the newatomization surface of the target body but larger than the surface ofthe receiving opening. Thus, although a high percentage of the wallsbounding the interior surface of the process space are coated, they arenot usefully coated, thereby still causing lower efficiency.

[0011] It is an object of the present invention to eliminate theabove-mentioned disadvantages and to improve efficiency. This object hasbeen achieved in a magnetron atomization source in accordance with thepresent invention by providing that the process space, apart from thereceiving opening for the at least one workpiece, is bounded essentiallyby the atomization surface, and reducing the surrounding non-atomizedresidual interior surface to a respective minimum which, duringatomization operation, ensures a stable plasma discharge.

[0012] As a result of the fact that, according to the present invention,the atomization surface of the target body essentially defines theprocess space, apart from the workpiece placed during the operation, asignificant improvement of the ratio between the atomized-off materialquantity and the material quantity deposited as a layer on the workpieceor the workpieces is achieved and results in a significant efficiencyincrease.

[0013] Preferred surface ratios are obtained according to the presentinvention by providing that the relationship of the residual interiorsurface, such as that of the receiving ring, and that of the atomizationsurface of the target body are such the former is less than or equal to50%. of the latter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] These and other objects, features and advantages of the presentinvention will become more readily apparent from the following detaileddescription when taken in conjunction with the accompanying drawingswherein:

[0015]FIG. 1 is cross-sectional schematic view of a currently preferredembodiment of magnetron atomization source according to the presentinvention; and

[0016]FIG. 2 is a view similar to FIG. 1 but supplemented with magneticcircuits.

DETAILED DESCRIPTION OF THE DRAWINGS

[0017] Referring now to FIG. 1, the magnetron atomization sourceaccording to the present invention comprises a target body 1 having, ina new condition, a conical atomization surface 3 a, or a concave mirrorshape 3 b, preferably in the shape of a calotte shell, so that, alreadyin its new condition with an atomization surface F₁, the target body 1is significantly thicker at the edge than in the center. Although in theillustrated preferred embodiment the target 1 is circular in top view(not shown) and therefore its concave shaped-in portion is rotationallysymmetrical, the target body 1 and the following constructional elementsof the source to be described later may, for certain uses, beconstructed to be symmetrical with respect to a single plane or to twoplanes. The target body 1 and therefore the additional constructionelements of the source preferably define a rectangular magnetron sourceor an elliptical or generally oval or, in the illustrated, preferredembodiment, a circular magnetron source.

[0018] In the illustrated circular magnetron source, the maximalthickness, d₁, of the target body 1 on its edge amounts to approximately50% of the target radius r₁. The target body 1 is embedded in aferromagnetic cup-shaped magnetic circuit housing 4 which defines acup-shaped magnet receiving space 5 which encloses the target body 1 onthe base side and on its upward-projecting lateral surfaces. Asurrounding receiving frame 9 is provided along the edge of the targetbody 1 and of the circular-ring-shaped end face 7 of the magneticcircuit housing 4 and is electrically insulated from the target body 1as well as the housing 4 at a dark space distance. The interior surfaceF₉ of the receiving frame 9 projects in a sloped manner from the edge ofthe target body 1 against the center axis A of the source inward anddefines a receiving opening 11 for a circular workpiece disk 13. In theillustrated embodiment, the ratio of the surface F₉ to the newatomization surface F₁ is:

F₉≦30% F₁.

[0019] The circular workpiece disk 13 is preferably a dielectric ormetallic workpiece disk, preferably the body of a storage disk to becoated, such as a magneto-optical storage disk, a video disk, an audiodisk such as a compact disk or CD. The periphery of the disk 13 rests atthe edge of the receiving opening 11 on the receiving frame 9 which,particularly in the case of CD processing, forms the peripheral maskingelement in order to prevent an atomization coating at the edge of thedisk and to obtain a transition which is as sharp as possible from thecoated surface to the uncoated edge.

[0020] The center of the target body 1 can be penetrated by a core 15,which is electrically insulated with respect thereto which, however, isnot necessary for implementing the source according to the presentinvention. For CD-coating and for coating most other optical storagedisks, the core 15 extends to the level of the receiving opening plane Ein order to mask the center of the workpiece disk 13. If unnecessary formasking or the like, the core 15, as indicated by the end surface 17,may be reduced in height or eliminated completely.

[0021] The target body 1 is placed by the magnetic circuit housing 4 ona negative cathodic potential. As indicated schematically by theselection units 23 a, 23 b, the core 15 as well as the receiving ring 9can be applied to the anode, such as the ground potential Φ₀ or toadjustable or fixedly given other reference potentials Φ_(v) or can eachbe operated in a floating manner. Preferably, the core 15 and the ring 9are applied to anodic potentials.

[0022] As illustrated, for example, by the insulation ring 9 c, two ormore parts 9 a, 9 b can constitute the receiving frame 9 and optionallybe operated electrically in different ways. For example, an anodicpotential can be applied to part 9 a, and part 9 b can be operated in afloating manner.

[0023] In the case of a circular workpiece disk 13 with a radius r₁₃,corresponding to a diameter φ13=2r₁₃, the following dimensioning of themaximal distance of the new atomization surface to the disk surface d₁₁₃to be coated has proven to be excellent:

d₁₁₃≧20% φ₁₃,

[0024] wherein the distance d₁₁₃, particularly in the case of normalpressure conditions of 10⁻³ to 10⁻¹ mbar during atomization coating,should not significantly fall below 25 mm.

[0025] Furthermore, the following dimensioning will preferably apply:generally, d₁₁₃≦50% φ₁₃, but preferably: d₁₁₃≦42% φ₁₃, and, mostpreferably, d₁₁₃≦35% φ₁₃.

[0026] The foregoing dimensioning is particularly true for theprocessing of circular-disk-shaped workpieces of diameters of from 50 mmto 150 mm, particularly 75 mm to 150 mm. If, however, the workpieces tobe coated are not of circular-disk-shape but, for example, are oval orrectangular, the indicated dimensioning directions with apply relativeto the smallest diameter φ_(k) of the respective workpiece. Furthermore,it has been found to be preferable, particularly for CD-coatingaccording to FIG. 1, that the target body radius r₁ is 30% to 40% largerthan the radius r₁₃ of the workpiece disk 13 to be coated.

[0027] The interior surface F₉ of the receiving ring 9 which isminimized in a sloped manner and which is neither usefully atomized norusefully coated and, with respect to plasma technology, ensures thedischarge stability in the edge area between the disk periphery and thetarget body edge, is preferably configured according to the followingdimensioning directions:

[0028] The distance Δ, which is perpendicular with respect to the axis Aor generally with respect to a plane of symmetry E_(s) and is bridged orspanned by the surface F₉, amounts, relative to the diameter φ₁₃ of acircular disk 13 or, more generally, with respect to the smallestdiameter Φ_(k) of a non-circular disk, as defined above, to, generallyΔ≦20% φ₁₃, but preferably to Δ≦10% φ₁₃, and currently is most preferablydimensioned at Δ≈15% φ₁₃.

[0029] It is also definitely possible to select the distance Δ to bezero. That is, the interior surface F₉ is configured to have onlycomponents parallel to the axis A or the plane E_(s).

[0030] The distance, a, bridged or spanned by the interior surface F₉,parallel to the axis A or the plane ES, irrespective of whether Δ is oris not larger than zero, and relative to the distance d₁₁₃ between thenew atomization surface center and the disk surface to be coated,amounts to, generally, 0≦a≦50% d₁₁₃, but preferably to 0≦a≦40% d₁₁₃, andis currently most preferably dimensioned at a≈30% d₁₁₃.

[0031] Furthermore, a system-side flange 25 is provided for mounting thesource according to the present invention. An electric insulation 29 isprovided between a source housing 27 with the flange 25 and the magneticcircuit/target body arrangement comprising the housing 4 and the targetbody 1. In addition, as illustrated schematically, the centric core 15is medium-cooled, preferably water-cooled, by way of a pipe system 31.The cooling of the receiving frame 9 takes place by way of the flange25.

[0032] The cathode/anode discharging distance may be operated by an AC-and DC-mixed supply, for example, by a timed DC, or may be operated onlyby DC. Layers may be deposited reactively or non-reactively, preferablyfrom electrically conducting target body material. As also illustrateddiagrammatically by the pipe system 33, the magnetic circuit housing 4and the target body 1 are medium-cooled, preferably water-cooled.

[0033] A working gas (for non-reactive atomization coating, this gas maybe a noble gas or for reactive atomization coating, this gas may be anoble gas with a reactive gas, the latter reacting with the materialatomized from the target body 1, and the coating taking place by areaction product) is preferably discharged by a schematicallyillustrated pipe system 35 in the core 15 via outlet openings 37 intothe process space as shown by the radially directed arrows.

[0034] In FIG. 2, which for reasons of clarity is the samerepresentation as FIG. 1, a currently preferably implementing magneticcircuit is entered in the housing 4. A ring of permanent magnets 40 isarranged in the area of the face 7 of the ferromagnetic housing 4. Inthe center and approximately on half the radius, r₁, of the atomizationsurface, additional permanent magnet rings 42 and 41 are provided.

[0035] As indicated, the polarities of the ring magnets are selectedsuch that, qualitatively, the magnetic field B illustrated in FIG. 2 iscreated above the atomization surface and essentially, as theatomization increases, maintains the same strength and the samedirection with respect to the momentary atomization surface. Naturally,it is also easily possible, for example, by way of a mechanicalfollowing of the magnet ring 40 and/or 41, to cause the magnetic fieldduring the atomization to follow the respective momentary atomizationsurface in an optimized manner. The face 7 is covered by a layer 8 of anon-ferromagnetic material (for example, an insulating material), suchas a high-temperature resistant and vacuum-suitable plastic material.This layer 8 is, on the side, disposed against the dark space 8 a and,on the other side, above the one magnetic pole N. As a result, parasiticplasma discharges and flashovers, which may be triggered in the darkspace by strong magnetic fields, are prevented.

[0036] With the magnetic field B constructed according to the presentinvention, it is also ensured that, also at the edge of the target body1, an atomization removal takes place as much as possible to largelyprevent an atomization accumulation there. Also, in the center of thetarget body 1, the zone in which no atomization removal takes place,also the amount of the atomized-on material is minimized.

[0037] The active elements 40, 41, 41 provided in the hollow space 5 andthe non-active elements, such as the iron housing 4 and the geometricalarrangement with its air gaps 44, contribute significantly to theconstruction of the magnetic field B of FIG. 2.

[0038] Because the receiving frame 9 shown in FIG. 1 can be electricallyoperated arbitrarily within wide ranges, and a center masking can beimplemented also by a center mask 50, without providing a core 15, it isnow possible with certainty to bring the frame 9 implementing the edgemasking in a changed construction and/or the center mask 50, asexplained in detail in German Patent Application 42 35 678, togetherwith the workpiece disk in the respective coating position.

[0039] With a magnetron sputter source implemented as shown in theexample, having a target diameter of 160 mm, a substrate diameter of 120mm, a target/substrate distance d₁₁₃ of 35 mm, a new atomization surfaceshape: concave, spherical shell with r=80 mm, a power supply of 15 kW,permanent magnets made of neodymium, ferrite, a pressure of approx. 10⁻²mbar, and a target material of Al (Mg, Si, Mn) service lives of 80,000coated CDs were achieved, corresponding to 220 kWh.

[0040] The specific coating rate, defined as the coating rate per powerunit (kW), in the case of the new atomization surface, amounted to 7nm/kws and, at the end of the service life, was still 4.5 nm/kws. Thecoating was carried out with a thickness of 55 nm. Here, 52% of thematerial atomized off the target body arrived as coating material on theworkpiece disks. The outer edge zone of the target body, which was notatomized off, amounted to 3 mm. In the center, this zone amounted toless than 1 mm, usually 0 mm. In these zones, the maximal atomizationquantity during the target life or service life amounted toapproximately 500 μm.

[0041] Thus, with the magnetron source according to the presentinvention, a high average coating rate is achieved with long servicelives while the surface coating is perfectly uniform and has highefficiency, whether defined as a coating quantity per atomized materialquantity or as a layer quantity per electric energy unit, in which caseall process parameters can be maintained essentially constant during theservice life of the target body. The specific coating rate was increasedvirtually to a factor of 2 compared with known sources.

[0042] Although the invention has been described and illustrated indetail, it is to be clearly understood that the same is by way ofillustration and example, and is not to be taken by way of limitation.The spirit and scope of the present invention are to be limited only bythe terms of the appended claims.

We claim:
 1. A magnetron atomization source, comprising a target bodyhaving an atomization surface which is mirror-symmetrically concavelyconstructed with respect to at least one plane, a magnetic circuitarrangement operable to generate a magnetic field over the atomizationsurface, including an anode arrangement, a receiving frame which extendsaround an edge of the target body and is electrically insulated withrespect thereto, which receiving frame has a receiving opening for atleast one workpiece to be coated, and, on the side of the source, aprocess space bounded substantially by the atomization surface of thetarget body and a surrounding non-atomized residual interior surface ofthe receiving frame, except for the receiving opening for the at leastone workpiece, wherein the surrounding non-atomized residual interiorsurface is minimized so that, during an atomizing operation, a stableplasma discharge is ensured.
 2. The source according to claim 1, whereinthe residual interior surface, F₉, and the atomization surface, F₁, ofthe target body, are related such that F₉≦50% F₁.
 3. The sourceaccording to claim 2, wherein F₉≦40% F₁.
 4. The source according toclaim 2, wherein F₉≦30% F₁.
 5. The source according to claim 1, whereinthe magnetic circuit arrangement is configured to be switchable to anelectric potential of the target body.
 6. The source according to claim1, wherein the atomization surface in a new state is constructed as oneof a paraboloid and spherical surface with respect to the receivingopening.
 7. The source according to claim 1, wherein the atomizationsurface is one of circular, oval and rectangular in plan view.
 8. Thesource according to claim 1, wherein the magnetic circuit arrangement isconfigured to maintain the atomization surface in a concave,continuously curved construction, during the atomizing operation.
 9. Thesource according to claim 1, wherein the magnetic circuit arrangement isconstructed such that a directional characteristic with respect toatomized-off particles of the atomization surface with respect to thereceiving opening is essentially maintained during the atomizingoperation.
 10. The source according to claim 1, wherein, for coating aworkpiece disk having a center to be covered, a masking core projectscentrally through the target body to a level of the receiving opening.11. The source according to claim 1, wherein gas outlets are arrangedcentrally with respect to the atomization surface to supply a processgas.
 12. The source according to claim 1, wherein a distance between theatomization surface in a new state and a plane of the receiving openingwith respect to a diameter, Φ_(k), of the receiving opening is 20% Φ_(k)≦d ₁₁₃.
 13. The source according to claim 1, wherein the distancebetween the atomization surface in a new state and a plane of thereceiving opening with respect to the diameter, Φ_(k), of the receivingopening is d₁₁₃≦50% Φ_(k).
 14. The source according to claim 13, whereind₁₁₃≦42% Φ_(k).
 15. The source according to claim 13, wherein d₁₁₃≦35%Φ_(k).
 16. The source according to claim 1, wherein the distance betweenthe atomization surface in a new state and a plane of the receivingopening is at least 25 mm.
 17. The source according to claim 16, whereinthe distance is between 30 mm and 55 mm.
 18. The source according toclaim 16, wherein the distance is between 30 mm and 35 mm.
 19. Thesource according to claim 12, wherein the receiving opening is circularand has a diameter of between 50 mm to 150 mm.
 20. The source accordingto claim 12, wherein the diameter is between 75 mm to 150 mm.
 21. Thesource according to claim 1, wherein a diameter of the atomizationsurface is between 30% and 40% larger than a diameter of the receivingopening.
 22. The source according to claim 1, wherein, for circularworkpiece disks, the receiving frame is parallel to a plane of thereceiving opening and has a width, Δ, of 0≦Δ≦10% φ_(k), wherein φ_(k) isthe smallest workpiece diameter.
 23. The source according to claim 22,wherein the width is 0≦Δ≦20% φ_(k).
 24. The source according to claim22, wherein the width is approximately 15% φ_(k).
 25. The sourceaccording to claim 1, wherein the residual interior surface of thereceiving frame perpendicular to a plane of the receiving opening has adepth, a, which, with respect to a maximal distance, d₁₁₃, between theatomization surface and the opening plane of the receiving opening, isdimensioned as a≦50% d₁₁₃.
 26. The source according to claim 25, whereina≦40% d₁₁₃.
 27. The source according to claim 25, wherein a≈30% d₁₁₃.28. The source according to claim 1, wherein at least a portion of thereceiving frame is one of applied to a reference potential and isoperated in a floating manner.
 29. The source according to claim 28,wherein the reference potential is variable.
 30. The source according toclaim 28, wherein the reference potential is anodic.
 31. The sourceaccording to claim 1, wherein a coating rate during service life of thetarget body decreases by less than 50% of an initial rate.
 32. Thesource according to claim 1, wherein an electric insulation is providedat least one high magnetic field intensity location to preventdischarges.
 33. A method of using an atomization source comprising atarget body having an atomization surface which is mirror-symmetricallyconcavely constructed with respect to at least one plane, a magneticcircuit arrangement operable to generate a magnetic field over theatomization surface, including an anode arrangement, a receiving framewhich extends around an edge of the target body and is electricallyinsulated with respect thereto, which receiving frame has a receivingopening for at least one workpiece to be coated, and on the side of thesource, a process space bounded substantially by the atomization surfaceof the target body and a surrounding non-atomized residual interiorsurface of the receiving frame, except for the receiving opening for theat least one workpiece, wherein the surrounding non-atomized residualinterior surface is minimized so that, during an atomizing operation, astable plasma discharge is ensured, comprising the step of providingstorage disks with atomization coating.